Generally, the designs of conventional UPSs can be classified into the following two categories.
UPSs with isolation generally use flyback conversion, or in some cases two-switch forward conversion.
UPSs without isolation may use a buck circuit as a step-down converter, or a buck-boost circuit as a step-down/step-up converter.
These conventional UPSs are designed with separately arranged chargers. In a UPS, the charger is an independent component regardless of how it is connected to the UPS.
FIG. 1 is a block diagram illustrating a first conventional UPS. As shown in FIG. 1, the UPS includes an input filtering circuit 1, a rectification circuit 2, an inversion circuit 3, a static transfer switch 4, an output filtering circuit 5, a control circuit 6, an auxiliary circuit 7, an DC/DC circuit A, a rechargeable battery B and a charging circuit C. Specifically, the input filtering circuit 1, the rectification circuit 2, the inversion circuit 3, the static transfer switch 4 and the output filtering circuit 5 are connected sequentially; and the output terminal of the input filtering circuit 1 is connected with the input terminal of the static transfer switch 4. The charging circuit C is connected between the rechargeable battery B and the output terminal of the input filtering circuit 1. The DC/DC circuit A is connected between the rechargeable battery B and the output terminal of the rectification circuit 2. The DC/DC circuit A, the rectification circuit 2, the inversion circuit 3 and the static transfer switch 4 are all controlled by the control circuit 6. Moreover, the rechargeable battery B powers the auxiliary circuit 7. In a mains power mode of the UPS, the rechargeable battery B is charged, by the mains power via the input filtering circuit 1 and then the charging circuit C. In a battery mode of the UPS, the rechargeable battery B is discharged, via the DC/DC circuit A to supply an input voltage to the inversion circuit 3.
FIG. 2 is a block diagram illustrating a second conventional UPS. As shown in FIG. 2, the second UPS differs from the first UPS in that: the charging circuit C is connected between the rechargeable battery B and the output terminal of the rectification circuit 2. Similarly, in a mains power mode of the UPS, the rechargeable battery B is charged, by the mains power via the input filtering circuit 1, the rectification circuit 2 and then the charging circuit C; in a battery mode of the UPS, the rechargeable battery B is discharged, via the DC/DC circuit A to supply an input voltage to the inversion circuit 3.
As can be seen, in the conventional UPSs, the rechargeable battery B is charged using an independent charging circuit C, causing a complex circuit structure and a higher cost.